The disclosed technology relates to certain polymethacrylates which impart a high viscosity index to lubricants, especially for internal combustion engines.
Acrylic and methacrylic polymers are known for use in lubricant compositions. For example, U.S. Pat. No. 3,397,146, Cupper et al., Aug. 13, 1968, discloses lubricating compositions comprising a mineral oil containing as a viscosity index improver-dispersant additive a polymer of a long chain alkyl acrylate or methacrylate, alkyl acrylate or methacrylate wherein the alkyl has from 1 to 4 carbon atoms, and acrylic or methacrylic acid, wherein the acid moieties of the polymer are neutralized with a 1-hydroxy-alkyl-2-alkyl or alkenyl imidazoline. The short chain alkyl acrylate or methacrylate will usually be from about 3 to about 15 weight percent, based upon weight of monomeric components.
U.S. Pat. No. 6,610,802, Roos et al., Aug. 26, 2003, discloses a process for synthesis of polymer compositions which may be used without further purification as additives in lubricating oils. In certain examples, a monomer mixture of DPMA:MMA of 85:15 is employed, where MMA is methyl methacrylate and DPMA is obtained by the reaction of ®Dobanol 25L (of Shell AG) with methyl methacrylate. The theoretical molecular weight is 20,000 g/mol.
U.S. Pat. No. 4,867,894, Pennewiss et al., Sep. 19, 1989, discloses polymers adaptable to use as pour point lowering additives for petroleum oils, said polymer comprising as comonomers therein (a) from 10 to 30 mole percent of methyl methacrylate, (b) from 10 to 70 mole percent of alkyl methacrylates having linear alkyl groups with from 16 to 30 carbon atoms in the alkyl group, (c) from 10 to 80 mole percent of alkyl methacrylates having linear alkyl groups with from 4 to 15 carbon atoms in the alkyl group and/or having branched alkyl groups with from 4 to 45 carbon atoms in the alkyl group, and (d) from 0 to 30 mole percent of a free-radically polymerizable nitrogen-containing monomer having dispersing action.
U.S. Pat. No. 6,331,603, Sivik et al., Dec. 18, 2001, discloses a nitrogen containing copolymer prepared by reacting (A) from about 55 to about 99.9% by weight of one or more alkyl acrylate ester monomers containing from 1 to about 24 carbon atoms in the ester alkyl group, wherein at least about 50 mole % of the esters contain at least 6 carbon atoms in the ester alkyl group, and (B) from about 0.1% to about 45% by weight of at least one (selected) nitrogen containing monomer. In an example, a container is charged with 57.5 parts methyl methacrylate, 12.7 parts butyl methacrylate, 226.5 parts each of C9-11 metacrylate [sic] and C12-15 methacrylate, 4.22 parts tert-dodecylmercaptan and 164.4 parts 85 neural paraffinic oil, followed by subsequent addition of VAZO-67 and 11.7! [sic] parts N-(-3-(dimethylamino)propyl)methacrylamide.
Related thereto is U.S. Pat. No. 6,969,068, Bryant et al., Oct. 19, 1999. It discloses a polymethacrylate ester based dispersant-viscosity modifier comprising units derived from (A) about 5% to about 75% by weight of alkyl acrylate ester monomers containing from 1 to 11 carbon atoms in the alkyl group; (B) about 25% to about 95% by weight of alkyl acrylate ester monomers containing from 12 to about 24 carbon atoms in the alkyl group; and (C) about 0.2% to about 20% by weight of a nitrogen containing monomer.
U.S. Pat. No. 6,124,249, Seebauer et al., Sep. 26, 2000, discloses viscosity improvers for lubricating oil compositions. A copolymer may comprise units derived from (a) methacrylic acid esters containing from about 13 to about 19 carbon atoms in the ester group, (b) certain methacrylic acid esters containing from 7 to about 12 carbon atoms in the ester group, and (c) at least one monomer selected from the group consisting of methacrylic acid esters containing from 2 to about 8 carbon atoms in the ester group, vinyl aromatic compounds, and nitrogen-containing vinyl monomers. Monomer (c) may be methyl methacrylate. When groups derived from monomer (c) are present, they comprise from about 0.2 to about 60 mole %, or 1 to about 25 mole %, of the units present in the polymer. In an example, a polymer is prepared from 280 parts C12-15 methacrylate, 80 parts 2-ethylhexyl methacrylate, and 40 parts methyl methacrylate.
The disclosed technology, therefore, addresses the problem of imparting a high viscosity index to a lubricant, thereby leading, in certain embodiments, to lubricants which provide improved fuel economy.